Many patients who have had surgical reconstruction of the right ventricular outflow tract come back to the doctor in need of reoperative surgical reconstruction of the right ventricular outflow tract (RVOT). Typically there is a history of previously operated tetralogy of Fallot (TOF) or pulmonary stenosis (PS) with such patients. Tetralogy of Fallot is a heart problem that is characterized by four defects in the heart: 1) ventricular septal defect (VSD), which is a hole between the two bottom chambers of the heart; 2) pulmonary stenosis, or a narrowing at or slightly below the pulmonary valve; 3) positioning of the aorta over the ventricular septal defect; and 4) the right ventricle being unusually muscular.
The predominant physiologic abnormality is pulmonary insufficiency (PI), but varying degrees of RVOT obstruction may also be present. It is generally believed that patients tolerate PI reasonably well. In some, however, the long term effects of PI and subsequent right ventricle (RV) enlargement and dysfunction result in poor exercise tolerance and increased incidence of arrhythmias. Numerous surgical options are available for these patients; however, the optimal timing and specific valve used for reconstruction remain uncertain. Less than ideal experience with heterograft RVOT reconstruction stimulated interest into alternative materials and techniques. Favorable experimental and clinical experience with reconstruction using PTFE monocusp valves spurred an interest to consider a new method of reconstruction with this material.
Increasingly, over the last several years, concerns regarding post-operative pulmonary insufficiency or insufficiency/stenosis have emerged. The previous adage that pulmonary insufficiency after valvectomy and/or transanular patching during repair of TOF was well-tolerated is now being questioned. Recent studies with more refined methods of evaluation utilizing echocardiogram or magnetic resonance imaging (MRI), as well as exercise testing, clearly show there is a relationship between pulmonary insufficiency and volume overload that results in right ventricular enlargement and dysfunction. Symptoms resulting from physical exertion are late and usually follow these objective changes in ventricular dysfunction and size. Additionally, life threatening ventricular arrhythmias seem to be associated with the more severe cases of pulmonary insufficiency and ventricular changes.
There is good evidence that RV enlargement and dysfunction is reversible following pulmonary valve replacement (PVR). However, recent evidence shows that there is a lack of significant recovery of RV indices following PVR in adults with long-standing pulmonary insufficiency. Therefore, the timing of PVR is of major importance in the overall maintenance of ventricular function and optimal long-term outcomes. Additionally, a program of aggressive PVR in conjunction with intraoperative cryoblation is effective in reducing both the size of the heart chamber and the potential for lethal arrhythmias in TOF patients with severe pulmonary insufficiency. It is also useful in decreasing the QRS duration, wherein “QRS” is a complex of waves on an echocardiogram that represent the time it takes for the ventricles to depolarize—the normal length of time being between 40 milliseconds and 160 milliseconds. In general, indications for PVR are evolving but currently include patients with moderate-severe PI/PS and 1) exertional symptoms, class II or greater, 2) RV systolic dysfunction and/or enlargement, 3) decreased exercise tolerance 4) ventricular arrhythmias and/or QRS duration greater than 160 milliseconds.
There is considerable debate as to what type of valve or reconstruction is optimal for the pulmonary position. A vast array of materials and methods have been utilized. Recent studies support the use of homografts, replacement valves from human donors, as well as stented and unstented heterograft valves, valves from non-human donors (pig valves are commonly used). However, despite definite early patient improvement, all reports for use of biologic valves show a significant incidence of recurrent valvar insufficiency and/or obstruction. A recent study of thirty-six patients utilizing homografts and heterografts for PVR noted that nine out of the thirty-four patients that were followed-up developed moderate to severe PI, and seventeen out of thirty-four developed significant obstruction within 80 months follow-up. Similarly, within 4.9 years, the incidence of homograft insufficiency was 50% mild, and 28% moderate-severe. Recent evidence suggests an immunologic basis for this early graft failure pattern.
In light of the above, it was thought that a non-immunologic, non-degenerating, and relatively durable material, such as PTFE, and a different method of insertion of the valve would provide more optimal results. Experience from 3-17 years utilizing a PTFE monocusp for RVOT reconstruction suggests reasonable long-term durability and freedom from degeneration. A larger study of 158 patients using a PTFE monocusp for RVOT reconstruction, with follow-up from 6 months to 8 years, demonstrated no stenosis, calcification, or embolization. There was, however, significant development of pulmonary insufficiency graded as moderate to severe by 35 months in this monocusp study.
The prior art discloses many types of heart valves, such in U.S. Pat. No. 5,344,442 issued to Deac, which discloses a cardiac valve designed to replace defective mitral valves in a patient's heart that comprises a plurality of flexible trapezoidal membranes each joined to another trapezoidal membrane to form a frustoconical annular body. Also, U.S. Pat. No. 4,340,977 issued to Brownlee, et al. for a catenary mitral valve replacement, which includes a mitral valve comprising a stent with a circular base and two upstanding, diametrically opposed struts that separate a pair of diametrically opposed arcuately shaped depressed reliefs. U.S. Pat. No. 5,500,015 issued to Deac for a cardiac valve comprising a plurality of membranes; U.S. Pat. No. 4,790,844 issued to Ovil, for a cardiac valve with an annular body having a bishop's miter shape with a cylindrical end and a pair of diametrically opposed triangular flap portions extending therefrom, and when the valve is inserted, the mitered end is free and the cylindrical end is attached to heart tissue; U.S. Patent Application Publication No. US2003/0181974 A1, filed by Xie, et al. for a bioprosthesis and method for suturelessly making same, which discloses a diamond-shaped frame to which a membrane is attached and wherein the frame is folded on itself and a slit cut into the folded side to allow fluid to flow through it; U.S. Pat. No. 6,682,559 B2, issued to Myers, et al. for a prosthetic heart valve that discloses a valve that includes a plurality of leaflets that are sewn together creating an annular structure which is then sutured into the heart; U.S. Patent Application Publication No. US2003/0163195 A1, filed by Quijano, et al. for a stentless atrioventricular heart valve fabricated from a singular flat membrane, which discloses attaching a membrane to a circumferential valve ring wherein the ring is sutured into an atrioventricular junction of a patient's heart.
There is also a need for low cost, safe valves for use in other parts of the vascular system such as the veins.